EP2161591A1 - Method and system for detecting the start of shooting - Google Patents

Abstract

A passive radar (3) coupled to opportunity transmitters (1, 2, 10) covers a given area of the space discretized in the radar in distance boxes. The passive radar (3) receives the signals emitted (21, 24) by the opportunity transmitters and reflected (22) by targets and detects the firing starts in each distance box where a target is detected by analyzing the associated Doppler boxes. at said distance box, a target being considered as corresponding to a firing start when the echo received from the target is focused on a distance box and distributed over several Doppler boxes.

Description

The present invention relates to a method and a system for detecting firing starts. It applies for example for the detection and location of firearm firing departures, such as including rifles, cannons or mortars.

To detect shooting origins in a theater of operations, various systems have been proposed and implemented. These systems are based on radar, acoustic sensors or optical sensors. Several methods can be used.
In a first known method, these systems detect a projectile and then reconstruct the trajectory to locate the origin of the shot.
In a second known method, these systems detect the shot itself. In this case, they use in particular acoustic or optical sensors.
These systems have certain disadvantages. For systems with acoustic or optical sensor bases, these systems do not make it possible to perform detection operations for all types of time or environment.
As far as conventional radar systems are concerned, they do not provide permanent surveillance of an area since these radars need to scan the space. Finally, radar systems require an accurate measurement of trajectory to go back to the origin of the shot, which complicates their implementation.

An object of the invention is to overcome the aforementioned drawbacks. For this purpose, the subject of the invention is a method for detecting a firing start from a weapon, said method using a passive radar coupled to opportunity transmitters covering a given area of the space discretized in the radar in distance cells, the passive radar receiving the signals emitted by the opportunity transmitters and reflected by targets and detecting the firing departures in each distance box where a target is detected by analyzing the Doppler boxes associated with said distance box, a target being considered as corresponding to a firing start when the echo received from the target is focused on a distance box and distributed over several Doppler boxes.
For example, a firing start is considered to be detected when the power of the received signal is greater than a given threshold over a number of Doppler boxes higher than a given N / K number, where N is the total number of Doppler boxes and K is a constant number. less than N. K is for example equal to 2.
Opportunity issuers may be broadcast or broadcast transmitters.
A fired start can actually be an explosion.

• un radar passif ;
• des émetteurs d'opportunité couvrant une zone donnée de l'espace discrétisé dans le radar en cases distances,

le radar passif comportant un circuit de réception recevant les signaux émis par les émetteurs d'opportunité et réfléchis par des cibles et des moyens de traitement détectant les départs de tir dans chaque case distance où une cible est détectée par analyse des cases Doppler associée à ladite case distance, une cible étant considérée comme correspondant à un départ de tir lorsque l'écho reçu de la cible est concentré sur une case distance et réparti sur plusieurs cases Doppler.
Avantageusement, le radar passif peut être aéroporté.The invention also relates to a system for detecting a firing start from a weapon, comprising at least:

• a passive radar;
• opportunity transmitters covering a given area of the space discretized in the radar in distance boxes,

the passive radar comprising a reception circuit receiving the signals emitted by the opportunity transmitters and reflected by targets and processing means detecting the firing departures in each distance box where a target is detected by Doppler box analysis associated with said distance box, a target being considered as corresponding to a firing start when the echo received from the target is concentrated on a distance box and distributed over several Doppler boxes.
Advantageously, the passive radar can be airborne.

• la figure 1, un exemple de réalisation d'un système selon l'invention sous forme simplifiée ;
• la figure 2, le principe de fonctionnement d'un système selon l'invention ;
• la figure 3, une illustration du principe de fonctionnement d'un radar passif.

• La figure 1 illustre de façon simplifiée un exemple de réalisation d'un système selon l'invention. Avantageusement, l'invention utilise un système radar passif, c'est-à-dire un système radar utilisant comme émetteurs des émetteurs d'opportunité 1, 2, 10 couplé à un système de réception radar 3 effectuant un traitement approprié des signaux, ce système de réception formant le radar passif. Ce radar 3 comporte notamment les moyens de réception et de traitement adaptés.
  Les émetteurs d'opportunité sont par exemple des émetteurs de radiodiffusion ou de télévision, d'autres types d'émetteurs sont possibles. Le système radar selon l'invention fonctionne ainsi en mode multistatique avec un système de réception 3 couplé avec des émetteurs 1, 2, 10 répartis.
  L'emploi de radars passifs pour cette fonction de détection et de localisation de départs de cibles n'était pas envisagé car les projectiles ont une section efficace radar faible dans les bandes de fréquence utilisées par ces radars fonctionnant typiquement dans des bandes de fréquences comprises entre 80 MHz et 2 GHz, c'est-à-dire avec des longueurs d'ondes comprises entre 2 mètres et 15 centimètres environ. Par ailleurs, le tireur est généralement fixe, donc non détectable par un radar.
  L'invention utilise avantageusement la signature Doppler d'une arme au moment du tir du projectile que cette arme tire. En d'autres termes, l'invention détecte l'arme au moment du tir par sa signature Doppler qui permet de la distinguer des échos fixes de l'environnement, par un filtrage passe-haut, et qui permet de la distinguer des échos mobiles par les caractéristiques particulières de cette signature Doppler. On bénéficie ainsi à la fois de la couverture permanente assurée par le radar passif, en l'occurrence les émetteurs d'opportunité 1, 2, et de la forte section efficace radar de l'arme comparée à celle du projectile.
• La figure 2 illustre plus précisément le principe de fonctionnement d'un système selon l'invention. Sur cette figure, un seul émetteur est représenté.
  Le radar passif 3 reçoit d'une part un signal en provenance directe 21 de l'émetteur d'opportunité 1 et d'autres part les signaux 22 réfléchies par des cibles potentielles 20 des signaux 21, 24 émis par l'émetteur. Il délivre, pour chaque direction de pointage de l'antenne 23, une carte distance-Doppler donnant pour chaque cellule distance-Doppler le niveau de signal reçu.
• La figure 3 illustre le fonctionnement classique d'un radar passif, par exemple le radar 3 utilisé dans un système selon l'invention. Il comporte des circuits de réception 31 connectés à l'antenne de réception 23.
  Le radar 3 effectue la corrélation du signal reçu à travers l'antenne 23, préalablement réfléchi par la cible 20, avec une réplique du signal attendu, pour une position et une vitesse d'une cible éventuelle. Puis il effectue cette opération de corrélation en parallèle pour tous les triplets position-vitesse-direction d'antenne, permettant de définir les niveaux de puissance reçue dans les cellules distance-Doppler de carte distance-Doppler définie dans le radar passif 3 et couvrant l'espace couvert par les radars d'opportunité.
  Le signal attendu est simplement constitué du signal 21 émis par l'émetteur 1, reçu directement par l'antenne 23, ou par une antenne auxiliaire, et convenablement retardé et décalé en fréquence porteuse pour reconstituer les décalages en distance et en Doppler. Ainsi le radar 3 comporte par exemple, en sortie des circuits de réception 31, un filtre 32 du signal direct 21 pour ne laisser passer que le signal 22 réfléchi par la cible. Il comporte également en parallèle de ce filtre, en sortie des circuits de réception 31, un circuit 33 réalisant la réplique du signal attendu, c'est-à-dire produisant le retard et le décalage précité sur le signal 21 reçu directement. La sortie de ce circuit 33 et la sortie du filtre 32 sont reliés à un circuit de corrélation 34. Ce dernier effectue ainsi, comme indiqué précédemment, la corrélation du signal reçu avec la réplique du signal attendu, pour une position et une vitesse de la cible dont est issu le signal réfléchi 22.
  Typiquement, la durée de signal utilisée pour cette opération de corrélation peut être de quelques centaines de millisecondes, conduisant à une résolution Doppler de quelques dizaines de Hertz et donc à une résolution en vitesse de l'ordre de quelque mètres par secondes, soit à titre d'exemple une vitesse de 5 m/s pour un radar fonctionnant à 100 MHz avec une durée cohérente de 300 ms.
  Le radar comporte, en sortie du circuit de corrélation 34, des moyens de traitement 35 effectuant la détection et la localisation d'un départ de tir.

Other characteristics and advantages of the invention will become apparent with the aid of the following description made with reference to appended drawings which represent:

• the figure 1 an embodiment of a system according to the invention in simplified form;
• the figure 2 the operating principle of a system according to the invention;
• the figure 3 , an illustration of the operating principle of a passive radar.

• The figure 1 illustrates in simplified manner an embodiment of a system according to the invention. Advantageously, the invention uses a passive radar system, that is to say a radar system using as emitters opportunity transmitters 1, 2, 10 coupled to a radar reception system 3 performing an appropriate processing of the signals. reception system forming the passive radar. This radar 3 comprises in particular the reception and processing means adapted.
  For example, opportunity transmitters are broadcasting transmitters or television transmitters, other types of transmitters are possible. The radar system according to the invention thus operates in multistatic mode with a reception system 3 coupled with transmitters 1, 2, 10 distributed.
  The use of passive radars for this function of detection and location of target departures was not considered because the projectiles have a weak radar cross section in the frequency bands used by these radars typically operating in frequency bands between 80 MHz and 2 GHz, that is to say with wavelengths between 2 meters and 15 centimeters. Moreover, the shooter is generally fixed, therefore not detectable by a radar.
  The invention advantageously uses the Doppler signature of a weapon at the time of firing of the projectile that this weapon fires. In other words, the invention detects the weapon at the time of the firing by its Doppler signature which makes it possible to distinguish it from the fixed echoes of the environment, by a high-pass filtering, and which makes it possible to distinguish it from the mobile echoes by the particular characteristics of this Doppler signature. This benefits both the permanent coverage provided by the passive radar, in this case the opportunity transmitters 1, 2, and the strong radar cross section of the weapon compared to that of the projectile.
• The figure 2 illustrates more precisely the operating principle of a system according to the invention. In this figure, only one transmitter is represented.
  The passive radar 3 receives on the one hand a signal coming directly from the opportunity transmitter 1 and on the other hand the signals 22 reflected by potential targets 20 of the signals 21, 24 emitted by the transmitter. It delivers, for each pointing direction of the antenna 23, a distance-Doppler map giving for each distance-Doppler cell the received signal level.
• The figure 3 illustrates the conventional operation of a passive radar, for example the radar 3 used in a system according to the invention. It comprises reception circuits 31 connected to the receiving antenna 23.
  The radar 3 performs the correlation of the signal received through the antenna 23, previously reflected by the target 20, with a replica of the expected signal, for a position and a speed of a possible target. Then it carries out this correlation operation in parallel for all the position-velocity-antenna direction triplets, making it possible to define the power levels received in the distance-Doppler map distance-Doppler cells defined in the passive radar 3 and covering the space covered by opportunity radars.
  The expected signal consists simply of the signal 21 emitted by the transmitter 1, directly received by the antenna 23, or by an auxiliary antenna, and suitably delayed and shifted in carrier frequency to reconstruct the distance and Doppler shifts. Thus the radar 3 comprises for example, at the output of the reception circuits 31, a filter 32 of the direct signal 21 to let only the signal 22 reflected by the target. It also comprises in parallel with this filter, at the output of the reception circuits 31, a circuit 33 producing the replica of the expected signal, that is to say producing the delay and the aforementioned offset on the signal 21 received directly. The output of this circuit 33 and the output of the filter 32 are connected to a correlation circuit 34. The latter thus performs, as previously indicated, the correlation of the signal received with the replica of the expected signal, for a position and a speed of the target from which the reflected signal originated 22.
  Typically, the signal duration used for this correlation operation may be a few hundred milliseconds, leading to a Doppler resolution of a few tens of Hertz and therefore to a speed resolution of the order of a few meters per second, or for example a speed of 5 m / s for a radar operating at 100 MHz with a coherent duration of 300 ms.
  The radar comprises, at the output of the correlation circuit 34, processing means 35 performing the detection and location of a firing start.

If the target 20 is a weapon, at the moment of firing, the signal 22 that it sends back is affected by a Doppler corresponding to its movement. When shooting this movement can be sinusoidal type. The Doppler can then be likened to a sinusoidal period of a typical length of a few hundred milliseconds. Its radial speed is therefore very rapidly variable, between +200 m / s and -200 m / s, for example. Therefore, on the distance-Doppler map, the echo of the target is well concentrated in a distance box, corresponding to the fact that the target remains in the space covered by this distance box, but this echo is distributed in speed, in because of the oscillation movements of the weapon due to firing. It can thus be identified as the echo of a weapon being fired, or an explosion, the signatures of the targets being, they, concentrated on the Doppler, due to the own displacement of the target.

Radar processing can be simple. It may for example consist, for each detected target, to examine the adjacent Doppler cells and to calculate the spread of the Doppler signature, that is to say the distribution of the Doppler boxes, by any usual index. Thus, this detection can for example be performed by counting the cells at the same distance where the level is greater than a predefined detection threshold in order to detect a movement of the "firing start" type. In practice, a target of "firing start" or "explosion" type is decreed as soon as the signal received is greater than the detection threshold on more than N / K Doppler boxes, for the same distance box. K is a constant quantity to be determined, for example K = 2 can be taken. Thus, the passive radar detects target departures and explosions by analysis of the corresponding Doppler boxes, in each distance box where a target is detected. Then it measures the extent of this Doppler signature, composed of these distance boxes and their power levels, by any known criterion, for example by counting the number of Doppler boxes where an echo is detected. A target is considered to be focused on a given distance box when most of the power received from that target is detected on that distance slot. A concentration threshold can be defined, corresponding to a given percentage of the total power received.

• opérations possibles par tous les temps et dans tous types d'environnements ;
• surveillance permanente de l'ensemble d'une zone ;
• possibilité d'observation directe de l'origine des tirs, ne nécessitant pas la mesure précise d'une trajectoire pour remonter à l'origine de tir.

Avantageusement, le radar passif 3 peut être aéroporté, de façon à assurer une meilleure visibilité des armes et des impacts au sol.The invention makes it possible to detect a firing start from a weapon on the ground or from an airborne weapon. Compared to conventional solutions, it brings the following advantages:

• operations possible in all weather and in all types of environments;
• permanent monitoring of an entire area;
• possibility of direct observation of the origin of the shots, not requiring the precise measurement of a trajectory to go back to the origin of shooting.

Advantageously, the passive radar 3 may be airborne, so as to ensure better visibility of weapons and ground impacts.

Claims (13)

A method of detecting a firing start from a weapon (20), characterized in that it uses a passive radar (3) coupled to opportunity transmitters (1, 2, 10) covering a given area of the space discretized in the radar in distance boxes, the passive radar (3) receiving the emitted signals (21, 24) by the opportunity transmitters and reflected (22) by targets and detecting the firing departures in each distance box where a target is detected by analyzing the Doppler boxes associated with said distance box, a target being considered as corresponding to a firing start when the echo received from the target is focused on a distance box and distributed over several Doppler boxes. Method according to Claim 1, characterized in that a firing start is considered to be detected when the power of the received signal (22) is greater than a given threshold over a number of Doppler boxes larger than a given N / K number, where N is the total number of Doppler boxes and K a constant number less than N. Method according to claim 2, characterized in that K is equal to 2. Method according to one of the preceding claims, characterized in that opportunity transmitters (1, 2, 10) are broadcasting transmitters. Method according to one of the preceding claims, characterized in that opportunity transmitters (1, 2, 10) are broadcasting transmitters. Method according to any one of the preceding claims, characterized in that the firing start corresponds to an explosion. System for detecting a firing start from a weapon (20), characterized in that it comprises at least: a passive radar (3); - opportunity transmitters (1, 2, 10) covering a given area of the space discretized in the radar in distance boxes, the passive radar (3) comprising a reception circuit (31) receiving the transmitted signals (21, 24) by the opportunity transmitters and reflected (22) by targets and processing means (32, 33, 34, 35). ) detecting the firing departures in each distance box where a target is detected by analyzing the Doppler boxes associated with said distance box, a target being considered as corresponding to a firing start when the echo received from the target is focused on a box distance and spread over several Doppler boxes. System according to Claim 7, characterized in that a firing start is considered to be detected when the power of the received signal (22) is greater than a given threshold over a number of Doppler boxes higher than a given N / K number, where N is the total number of Doppler boxes and K a constant number less than N. System according to claim 8, characterized in that K is equal to 2. System according to one of Claims 7 to 9, characterized in that opportunity transmitters (1, 2, 10) are broadcast transmitters. System according to one of claims 7 to 10, characterized in that opportunity transmitters (1, 2, 10) are broadcast transmitters. System according to any one of claims 7 to 11, characterized in that the firing start corresponds to an explosion. System according to any one of claims 7 to 12, characterized in that the passive radar (3) is airborne.

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